In the production of semiconductor devices and liquid crystal displays, rapid progress has recently been made in miniaturizing of a pattern with the progress of a lithography technology. As a technique for miniaturizing of the size, shortening of the wavelength of an exposure light source is generally performed. Specifically, while ultraviolet rays typified by g-ray and i-ray have hitherto been used, mass production of semiconductor devices using a KrF excimer laser or an ArF excimer laser has recently started. Also, a study on F2 excimer laser having a shorter wavelength than that of these excimer lasers, electron beam, EUV (extreme ultra violet), and X-rays have been made.
As one of pattern forming materials capable of forming a pattern having a fine size, a chemically amplified resist containing a base resin component having a film forming ability and an acid generator component which generates an acid upon exposure is known. The chemically amplified resist includes, for example, a negative chemically amplified resist in which alkali solubility decreases upon exposure, and a positive chemically amplified resist in which alkali solubility enhances upon exposure.
A polymer is conventionally used as a base material component of the chemically amplified photoresist and, for example, polyhydroxystyrene (PHS), a PHS-based resin in which a portion of hydroxyl groups is protected with an acid dissociable dissolution inhibiting group, and a copolymer derived from a (meth)acrylate ester are used.
However, in the case of forming a pattern using such a pattern forming material, these arises a problem such as roughness on the top face of the pattern or the surface of the side wall. Such a problem becomes more serious as the pattern size decreases. For example, it is an object to form a fine pattern of several tens of nanometers in lithography using EUV or EB, and therefore there is required ultra-low roughness which exceeds conventional pattern roughness.
However, a polymer used commonly as a base material has so large molecular size (mean square radius per molecule) as several nanometers. In the developing step of pattern formation, since dissolution behavior of the resist to a developing solution is commonly conducted at a molecular unit of a base material component, it is very difficult to further reduce roughness as long as the polymer is used as the base material component.
To solve such a problem, a resist using a low molecular material as a base material component is proposed as a material which is developed so as to attain ultra-low roughness. For example, Japanese Unexamined Patent Application, First Publication No. 2002-099088 and Japanese Unexamined Patent Application, First Publication No. 2002-099089 proposes a low molecular material having an alkali soluble group such as hydroxyl group, a portion or all of which is protected with an acid dissociable dissolution inhibiting group. It is anticipated that such a low molecular material has a low molecular weight and therefore has a small molecular size and can reduce roughness.
However, it is actually difficult to form a fine pattern, for example, a fine pattern having a size of 90 nm or less in a level, which enables practical use, using such a material. For example, there is a problem that a pattern itself cannot be formed or, if the pattern is formed, the patter has very poor shape.